Overspeed protection system for a turbo-generator unit

ABSTRACT

A vacuum breaking valve on a condensing turbine is operable by a controller responsive to losses of load on the generator to admit a pre-determined quantity of air to the condenser to reduce vacuum and the acceleration of the turbo-generator unit upon loss of load by the generator.

United States Patent [191 Tapper et a1.

111 3,750,395 Aug. 7, 1973 OVERSPEED PROTECTION SYSTEM FOR A TURBO-GENERATOR UNIT [75] Inventors: Donald N. Tapper, Media; James M. Fieglein, Clifton Heights, both of Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Oct. 22,197!

[21-] Appl. No.: 191,583

[52] U.S. Cl. 60/73, 60/96 290/40 B,

2,066,151 12/1936 Johnson 60/65 2,144,550 1/1939 Sheppard 290/2 3,097,487 7/1963 Clark 160/70 3,572,036 3/1971 Beckman et al. 60/105 Primary I ExaminerMartin P. Schwadron Assistant Examiner-H. Burks, Sr. Att0rney-A. T. Stratton, F. J. Balhr, Jr. et a1.

57 ABSTRACT A vacuum breaking valve on a condensing turbine is operable by a controller responsive to losses of load on the generator to admit a pre-determined quantity of air to the condenser to reduce vacuum and the acceleration of the turbo-generator unit upon loss of load" by the [56] ReferencesCited generator.

UNITED STATES PATENTS i 1 1,910,619 5/1933 Lysholm et al. 60/70 4 Claims, 2 Drawing Figures MOISTURE SEPARATING FROM REHEATER 5 STEAM GENERATOR V V TURBINE GENERATOR CONDENSER f7 TO STEAM G NERATOR L AD- PATENTEU MIR 7 GENERATOR LOAD CONDENSER MOISTURE SEPARATING REHEATER TURBINE R O T. A M 5 TE 86 FROM CONTROLLER GENERATOR STEAM FIG. I.

CONTROLLER OVERSPEED PROTECTION SYSTEM FOR A TURBO-GENERATOR UNIT BACKGROUND OF THE INVENTION and associated piping inherently store a large quantity of steam and water, which if allowed to expand through the turbine after the generator has lost its load, will accelerate the turbine, causing it to overspeed. Stop valves and intercept valves can be installed between the reheater and turbine, and operate to relieve this problem; however, they are expensive to manufacture andto install.

SUMMARY OF THE INVENTION In general, a turbo-generator unit, when made in accordance with this invention, has a steam turbine, a generator, a condenser and a device responsive to loss of load on the generator to reduce the vacuum in the condenser a predetermined amount to reduce the acceleration of the turbine due to loss of load on the generator.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and the advantages of this invention will become more apparent from reading the following detailed description in connection with the accompanying drawings, in which FIG. 1 is a flow diagram, showing a turbo-generator made in accordance with this invention; and

FIG. 2 shows an enlarged elevational view of an overspeed protection system operable to reduce the vacuum in the condenser a predetermined amount.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, FIG. 1 shows a flow diagram of a turbo-generator unit 1 having a turbine 3, which has a moisture-separating reheater 5 disposed between groups of stages therein, a condenser 7 for condensing exhaust steam from the turbine 3 and a generator 9 disposed on a single shaft 11 with the turbine 3.

Motive steam from a steam generator (not shown) flows through a stop valve 13 and into the turbine 3, wherein it is expanded through a group of stages and is reheated in the moisture separating reheater 5 and expanded through another group of stages and then exhausted to the condenser 7, wherein the steam is condensed, resulting in a vacuum in the condenser. The condensate formed in the condenser 7 is pumped back to the steam generator, forming a closed cycle.

The moisture separating reheater 5, hereinafter referred to on a reheater, is connectedto the turbine 3 by unobstructed or valveless conduits or pipes 14 to provide a minimum pressure drop and low cost installation.

A' sudden loss of load on the generator 9 causes the steam in the high pressure stages of the turbine 3 and in the reheater 5 to expand through the low pressure stages of the turbine 3 to the condenser 9, causing the turbine to accelerate and overspeed, which may result in damage to the turbo-generator unit.

A controller or load drop anticipator l5 responsive to loss of load operates stop valve 13 and a vacuum breaker valve 17 to stop the flow of motive steam to the turbine and simultaneously reduce the vacuum in the condenser a predetermined amount to reduce the acceleration of the turbine resulting from loss of the load on the generator.

To reduce the vacuum by a predetermined amount, the controller opens the valve 17 for a predetermined period, and then closes the valve, admitting a quantity of air sufficient to raise the pressure in the condenser approximately 1 k to 10 inches of mercury (Hg) with the optimum range being 3 to 5 inches Hg. This reduction in condenser vacuum is sufficient to reduce the acceleration of the turbine caused by the expansion of steam stored in the reheater, and thus limit the speed the turbine will attain after a sudden loss of load to a safe value.

As shown in FIG. 2, the vacuum breaker valve 17 is disposed ina. conduit 19, which places the condenser 7 in communication with atmospheric air. A filter or screen 21 is provided to prevent trash from entering the condenser 7.

The valve 17 is aquick-operating pneumatic or hydraulic fluid operated valve, and is arranged to open when supplied with pressurized fluid and close when the pressurized fluid is bled off. With such an arrangement the valve fails closed, that is,'on a loss of fluid pressure the valve remains closed, preventing the valve from opening during normal operation, if the fluid pressure were lost. In the pneumatic system shown in FIG. 2, a solenoid valve 23 is disposed in a supply conduit 25 and is operated to open a response to loss of load as sensed by the controller 15. The controller has a time delay disposed therein, which deactivates the solenoid valve 23 after a predetermined period, resulting in the valve 17 closing. Thus, the valve 17 is open for a predetermined time, admitting a determinable amount of air into the condenser, sufficient to reduce the vacuum approximately 1 k to 10 inches of mercury.

Such a system, with a stop valve operable to shut off motive steam and a vacuum breaker adapted to reduce the condenser vacuum a predetermined amount in response to loss of load, advantageously provides reliable overspeed protection at a minimum cost.

What is claimed is:

l. A turbo-generator having a steam'turbine, a generator, a condenser, and means responsive to loss of load on the generator to reduce the vacuum in the condenser a predetermined amount to reduce the acceleration of the turbine due to loss of load on the generator, said vacuum reducing means comprises a conduit, placing the condenser in communication with atmospheric air and a fast-operating valve operable by a controller responsive to loss of load on the generator.

2. A turbo-generator as set forth in claim 1, wherein the controller is responsive to the loss of load on the generator to open the. valve and upon expiration of a predetermined period of time to close the valve.

3'. A turbo-generator as set forth in claim 1, wherein theturbo-generator has a reheater disposed between groups of stages in the turbine and-unobstructed conduits connecting the reheater to the turbine.

4. A turbo-generator as set forth in claim 1, wherein the vacuum reducing means is adapted to reduce the vacuum in the condenser generally between l k inches and 10 inchesof Hg.

i i i i O 

1. A turbo-generator having a steam turbine, a generator, a condenser, and means responsive to loss of load on the generator to reduce the vacuum in the condenser a predetermined amount to reduce the acceleration of the turbine due to loss of load on the generator, said vacuum reducing means comprises a conduit, placing the condenser in communication with atmospheric air and a fast-operating valve operable by a controller responsive to loss of load on the generator.
 2. A turbo-generator as set forth in claim 1, wherein the controller is responsive to the loss of load on the generator to open the valve and upon expiration of a predetermined period of time to close the valve.
 3. A turbo-generator as set forth in claim 1, wherein the turbo-generator has a reheater disposed between groups of stages in the turbine and unobstructed conduits connecting the reheater to the turbine.
 4. A turbo-generator as set forth in claim 1, wherein the vacuum reducing means is adapted to reduce the vacuum in the condenser generally between 1 1/2 inches and 10 inches of Hg. 